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Mirroring pool


Michael Carson

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I've got a pool consisting of a 10TB + 3TB disk called Primary Pool.

I've got another pool consisting of duplicate hardware - 10TB + 3TB disk - called Backup Pool.

I essentially just wanted the Primary Pool to be duplicated on the Backup Pool in a mirroring fashion. 

My original thought was that I could just create a new pool and add the above pools to it and turn on duplication of the pool but the new pool didn't reflect the contents of the primary pool.   So, I eventually just added the Backup pool to the Primary Pool which expanded the primary pool to 26TB and turned on pool duplication.  I'm not sure that this is doing what I want it to do though. Maybe I should have just added the drives from the backup pool to the primary pool and not worry where the files ended up residing as long as duplication x2 was on.  

What's the "proper" way of doing this?

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You can create one Pool with the 4 HDDs and have x2 duplication (although, if one of the 10TB HDDs fails, then you could run into the issue that the Pool can not provide x2 duplication anymore because there is only 6TB of other HDDs remaining).

Another way of organising things is to create two Pools of 10TB+3TB each, no duplication and create a third Pool consisting of the other 2 with x2 duplication. One reason to do it like this could be if you want to run a backup solution that does not run (well) of a virtual disk (which is what any Pool is) that does not support VSS. Moreover you are assured that all files reside only one time on any set of two HDDs (or the number of HDDs that is in one the underlying Pools).

I think this second method is what you tried to do. The reason it did not work is that the data needs to be transferred from the underlying Pool to the MOAP (Mother Of All Pools). With a setup that uses Hierarchical Pooling, you actually end up with three Pools and you can read&write to each of them.

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So, how does this work logistically?  Maybe the following:

  1. Create a primary pool of 10TB + 3TB
  2. Create a backup pool of 10TB + 3TB
  3. Create a mother of all pools containing just the backup pool
  4. Copy all information from primary pool to mother of all pools
  5. Delete information from primary pool and add it to the mother of all pools
  6. Enable duplication on mother of all pools

How does this help with backup solutions that don't like pools? Do you go down to the underlying disks themselves in the backup pool and just back them up?

Right now, I have a single pool consisting of all the HDD's with pool duplication turned on. If a 10 TB HDD dies, I should still have all of my files on the remaining drives but duplication stops if I have more than 8TB of information in the pool. 

  • 10TB Drive dies: 26TB - 10TB = 16TB/2 = 8TB max of duplication
  • 3TB drive dies:    26TB - 3TB = 23TB/2 = 11.5TB max of duplication

Unless I'm missing something, it doesn't really matter with drivepool where the data resides.  If duplication is turned on, I can lose a drive and still have all of my data.  The bad drive just has to be removed from the pool and another of equal or larger size is needed to replace it (or multiple smaller drives adding up to the size of the drive lost).  I guess I just need to stop being hung up on the RAID paradigm.

What's a good backup program that works with a Drivepool volume rather than having to go to the base disks?

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I think I understand the backup reasons now for doing the two 13TB pools.  There don't seem to be a lot of good tools for doing backup of the pool so if you can backup the individual drives without any duplication then that's the way around backing up the pool. 

The best backup scheme that I've come up with so far is to use freefilesync on the pool.   For non-pooled drives,  I've been using Terabyte's IFW. 

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One Pool Scenario: If a 10TB HDD fails then you can only store 6TB duplicated. This is because duplication requires both/each duplicate to be stored on a different physical HDD and after 6TB (duplicates on both 3TB HDDs and the 10TB HDD) you have no duplicate space left.

Wrt Backup, yes. All data is stored in in plain NTFS format and I indeed backup one set of underlying HDDs. I run Windows Server 2016 Essentials and use Windows Server Backup. Not everyone is a fan but it has as yet never failed me (and I have had to recover).

On your scenario, item #4: No. What you need to understand is where/how pooled files are stored. Let's talk about the first Pool on HDDs, say, F: and G:. You can still store files on F: outside of the Pool. On F:, you will find a (hidden) PoolPart.* folder. Anything stored in this folder is part of Pool 1. Same on G:. If you now add Pool 1 to the MOAP, then within that PoolPart.* folder, you will find another PoolPart.* folder. Anything stored in there is part of MOAP. Althoug you can copy/delete, this actually takes a lot of time. The easier way to go about this is:
4. Enable duplication on MOAP.
5. Stop the DrivePool Service
6. On F:\ Move all files from the upper PoolPart.* folder to the underlying PoolPart.* folder
7. Same on G:\
8. Start DrivePool Service

The advantage of steps 6 and 7 is that moving files onthe same HDD is very fast as it does not actually entail a read/write/delete of the files but simply rewrites the folder/location information. After step 8, DP will find that in MOAP, files are not duplicated and then perform a balancing/duplication pass. It will take some time depending on size and number of files but it will work well.

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